1. Field of the Invention
The present invention relates to a throttle positioner for use with a carburetor of an internal combustion engine and, more particularly, a novel structure of the throttle positioner which obviates some inherent drawbacks in the conventional throttle positioner.
2. Description of the Prior Art
When an automobile is decelerated while it is running, the amount of uncombusted components in the exhaust gas significantly increases. In order to solve this problem, a device which is called a throttle positioner has been proposed. The throttle positioner operates to hold a throttle valve at a predetermined opening position where it is slightly opened from its idling position when an automobile is decelerated, thereby maintaining a predetermined minimum amount of air supply through an intake manifold, thus avoiding heavy emission of uncombusted material in the exhaust gas.
Conventionally, the throttle positioner comprises a diaphragm means, a throttle positioning lever adapted to be driven by said diaphragm means so as to rotate between first and second rotary positions, and a throttle driving lever mounted on a rotary shaft of a throttle valve and adapted to engage a tip of said throttle positioning lever so as to hold return of the throttle valve at a predetermined opening position when said throttle positioning lever is in said first rotary position while disengaging from said tip of said throttle positioning lever so as to permit full return of the throttle valve to an idling position when said throttle positioning lever is in said second rotary position. The diaphragm means is adapted to be selectively supplied with atmospheric pressure or vacuum thereby rotating said throttle positioning lever to said first or second rotary position in order to selectively effect the operation of the throttle positioner when required. Manifold vacuum is generally employed as the vacuum to be selectively supplied to the diaphragm means. The manifold vacuum is taken out from a vacuum port provided at a position where the mnifold vacuum always exists. The vacuum thus obtained is selectively supplied to the diaphragm means under the control of an electro-magnetic valve adapted to operate according to the running condition of the automobile. Or alternatively, the manifold vacuum is taken out from a vacuum port which opens close to a tip end portion of a throttle valve rotated at its fully closed position, the vacuum taken out from the port being supplied to the diaphragm means without interposition of an electro-magnetic valve but generally with interposition of means to delay transmission of the vacuum. In the latter constitution, when the throttle valve is substantially opened, the vacuum port is located upstream of the throttle valve and, therefore, the port is not applied with any substantial manifold vacuum. In this condition, therefore, the diaphragm means is released thereby rotating the throttle positioning lever toward said first rotary position. If the throttle valve is rapidly closed in this condition, the throttle driving lever engages the throttle positioning lever thereby positioning the throttle valve at a throttle positioner pre-set opening. When the throttle valve is thus positioned at the throttle positioner pre-set opening, the vacuum port is located downstream of the throttle valve, whereby the port is applied with a substantial manifold vacuum, said vacuum being gradually supplied to the diaphragm means through said vacuum delay means. Therefore, the diaphragm means is gradually tightened to rotate the throttle positioning lever towards said second rotary position and, after the lapse of a predetermined time, the throttle driving lever is released from the engagement with the throttle positioning lever and the throttle valve is permitted to return to its idling position.
In the conventional throttle positioner, however, in order to accomplish the operation that the throttle driving lever is engaged by the throttle positioning lever to effect the throttle positioning action, the throttle driving lever must approach the throttle positioning lever rotated at its first rotary position from a distant position or, in other words, from a position where the throttle valve is substantially opened. This condition does not cause any problem when the throttle valve is rapidly returned toward its closing position from its substantially opened position as in the case where an automobile is decelerated from its normal running condition because, in this case, the throttle positioning lever certainly approaches the tip end of the throttle positioning lever rotated at its first rotary position. However, when the throttle positioner is utilized, in addition to its original object of preventing emission of a large amount of uncombusted components into the exhaust gas in a decelerating operation, to increase the output of the engine in its idling operation for the purpose of ensuring stable idling operation when an air conditioner is driven by the engine in the summer season, there occurs an inconvenience in that after the manifold vacuum has been supplied to the diaphragm means, by for example, switching-over of an electro-magnetic valve, the accelerating pedal must be stepped on so that the throttle driving lever is once removed from interference with the throttle positioning lever thereby permitting the throttle positioning lever to return to its first rotary position before the effective throttle positioning engagement between the throttle positioning lever and the throttle driving lever is obtained.